This invention relates to an ion-conductive polymer electrolyte.
As an ion-conductive polymer electrolyte, there has been known following compounds. For example, an organic polymer electrolyte of polyethylene oxide (PEO) type; an organic polymer electrolyte having a multifunctional polyether molecular structure prepared by a randam copolymerization of ethylene oxide portion and propylene oxide portion (Japanese Laid-Open Patent Publication No. 249,361 of 1987); a solid polymer electrolyte comprising an ethylene oxide copolymer containing an ionic compound in dissolved state (Japanese Laid-Open Patent Publication No. 83,249 of 1986); and an ion-conductive polymer electrolyte in which a high polymer solid substance having plasticity is further constituted substantially with a branched-chain of a homopolymer or copolymer which is thermoplastic and has no crosslinkage (Japanese Laid-Open Patent Publication No. 98,480 of 1980).
However, those conventional ion-conductive polymer electrolytes have the following problems.
First, the organic polymer electrolyte of polyethylene oxide type shows a relatively good lithium-ion conductivity in the temperature range of not lower than 40.degree. C., but the characteristic is lowered rapidly at the room temperature range of about 25.degree. C. Accordingly, it is difficult that the electrolyte is used for various electric applications.
The organic polymer electrolytes described in Japanese Laid-Open Patent Publication No. 249,361 of 1987 do not show rapid lowering of the lithium-ion conductivity at the room temperature range of about 25.degree. C., but the lowering proceeds at a temperature of not higher than 0.degree. C. which is considered as a practical temperature range. Therefore, a practical ion-conductivity can not be obtained.
The organic polymer electrolyte described in Japanese Laid-Open Patent Publication No. 83,249 of 1986 is an organic polymer prepared by a random-copolymerization of ethylene oxide with the other monomer. The structure of the organic polymer resultantly becomes amorphous as a result by the random-copolymerization, but the product quality tends to be unstable since the structure of the organic polymer does not become amorphous sufficiently.
Further, since the organic polymer electrolyte described in Japanese Laid-Open Patent Publication No. 98,480 of 1980 is thermoplastic, a film formed with it is limited only to be simple and a good adhesion of the film can not be obtained.
The object of the present invention is to solve such problems as described above and to provide an ion-conductive polymer electrolyte which shows an excellent and stable ion conductivity at low temperature and can be easily handled.